A battery is an electrochemical storage device, which stores electrochemical energy for later release as electrical energy. Batteries can be either primary or secondary batteries. A primary battery irreversibly consumes at least one chemical entity in the process of producing electrical energy, while a secondary battery reversibly consumes at least one chemical entity. In the secondary battery, the consumed chemical entity is restored (or converted) to its original chemical state by supplying electrical energy to the battery. The restoring of the consumed chemical entity to its original state, is typically referred to as re-charging. The electrical energy is supplied to the battery from another source.
Lithium-ion batteries are a type of secondary batteries. A lithium-ion battery has three main components: an anode, a cathode, and an electrolyte. The anode is typically made of graphite, while the cathode is typically made a one of the following: a layered oxide (such as lithium cobalt oxide), a polyanion (such as lithium iron phosphate) or a spinel (such as, lithium manganese oxide).
The electrolyte is typically an organic solvent containing a lithium salt. The electrolyte carries the electrical current (that is, carries lithium cations [Li+]) between the cathode and anode when the lithium-ion battery is being charged or discharged. Organic solvents (such as, ethers) are used, instead of water, since lithium-ion battery voltages are generally greater than the potential at which water electrolyzes. Common lithium salts used within the electrolyte are: Li[PF6], Li[BF4] AND Li[ClO4]. Optionally, the electrolyte also contains a solid electrolyte interphase forming material, which forms a solid layer called the solid electrolyte interphase (SEI). The solid electrolyte interphase layer is typically formed during the first battery charging. The SEI layer, while still sufficiently conductive to lithium ions, is electrically insulating and prevents further decomposition of the electrolyte after the first battery charging. Ethylene carbonate is an example of a solid electrolyte interphase forming material.
During the charging and discharging processes lithium-ions migrate into and/or out of the anode and cathode. The process of the lithium-ions migrating into the anode or cathode is referred to as intercalation. And, the process of the lithium-ion moving out of the anode or cathode is referred to as de-intercalation. During lithium-ion battery discharge, lithium-ions are de-intercalated (that is, extracted) from the anode and intercalated (that is, inserted) into the cathode. And, when the lithium-ion battery is charged, the lithium-ions are intercalated into the anode and de-intercalated from the cathode. Useful electrical work is provided when electrons flow from the lithium-ion battery through an external electrical circuit connected to the lithium-ion battery.
Electrons are generated or consumed by the anodic and cathodic half-cells. More specifically, electrons are generated when the metal oxide-containing cathode is oxidized and lithium-ions are de-intercalated during charging. The cathodic half-cell reaction is illustrated by the chemical equation (1), as follows:LiMOLi(1-x)MO+xLi++xe−  (1)where MO denotes a metal-containing oxide (such as, CoO2, MnO2, and FePO4). Equation (1), as written, depicts the cathodic charging process. More specifically, the metal oxide (MO) is oxidized during charging from MOn+ to MO(1+1)+ and reduced during discharging from MO(n+1)+ to MOn+. The reverse of equation (that is, the process proceeding from right-to-left) depicts the cathodic charging process, where electrons are consumed when the metal oxide-containing cathode is reduced and lithium-ions are intercalated.
The anodic half-cell reaction can be illustrated by chemical equation (2), as follows:xLi++xe−+AMLix(AM)  (2)where AM represents the anodic material, such as graphite.
The internal resistance, voltage, energy density, power density, lifetime and safety level of the lithium-ion battery is substantially determined by the anode, cathode and electrolyte of the lithium-ion battery. The lithium-ion battery specific energy density can range from about 150 to about 200 Wh/kg. And, the specific power density can range from about 300 to 1,500 W/kg. The nominal cell voltage of the lithium-ion battery can range from about 3.0 to about 4.0 volts. The internal resistance of a typical lithium-ion cell is from about 250 mOhn to about around 450 mOhm.
As lithium-ion battery applications expand from small consumer electronic applications (such as, hearing aids) into larger consumer electronic (such as, laptops, cell phones, and hand-help electronic devices) and into even more demanding military, automotive, and aerospace applications, greater cycle life and performance improvements are needed. Specifically, improvements in power output and decreased internal resistance will be needed. In other words, more active anode, cathode and/or electrolytes are needed to produce lithium-ion batteries having improved energy-to-weight ratios, less maximum energy capacity loss, and a slower loss of charge during storage. More specifically, for lithium-ion batteries, an increase of power density without a decrease of energy density is needed. This means that a high power lithium-ion battery with a high-energy storage capacity is required. This has been a long sought after solution within battery technology for high-power battery applications in the areas of transportation technologies, uninterruptable power systems, and power tools, where high charge/discharge rates are required.